.1. DAVIDSOX. 
O.jS 
in the laboratory orchard^ (i) at the end of first season of 
infection, (ii) during the second season after infection with 
S, lanigera. 
A remarkable feature of aphids is the extraordinary 
Text-fig. A. Text-fig. B. 
4 
Text-fig. A. — Schizoneura lanigera attacking branch of young 
apple tree (Cox's orange pippin), the second season after infection. 
(Photograph taken from experiment trees in the laboratory 
orchard.) 
Text-fig. B. — Schizoneura lanigera establishing itself on an 
injured branch of an apxile tree. 
numbers of young that may be produced during a season, 
lieproduction is largely carried on by parthenogenetic females, 
which give rise to numbers of living young. Throughout 
successive generations a series of different forms may be 
produced, thus resulting in a complex polymorphism. These 
